1. Field of the Invention
The present invention relates to a process of forming an electrode for a chip-like electronic part and a holder for a chip-like electronic part, particularly to a process of forming an electrode comprising a conductive paste on an outer surface of a chip-like electronic part and a holder for a chip-like electronic part preferably used in carrying out the process.
2. Description of Related Art
FIG. 18 shows a perspective view of a chip-like electronic part 1, particularly a three terminal capacitor. End electrodes 2 and 3 are formed on respective end portions of the chip-like electronic part 1 and central electrodes 4 are formed at the central portion thereof.
Although not illustrated, first and second groups of inner electrodes are arranged alternately inside the chip-like electronic part 1 with the inner electrodes of the first group extending to the end electrodes 2 and 3 and the inner electrodes of the second group extending to the central electrodes 4. Accordingly, electrostatic capacitances formed between the inner electrodes of the first group and the inner electrodes of the second group can be taken out between the end electrode 2 or 3 and the central electrodes 4. The chip-like electronic part 1 is used to, for example, remove noise on a signal line by coupling the end electrodes 2 and 3 to the signal line and grounding the central electrodes 4.
As shown in FIG. 18, the central electrodes 4 extend across two opposing side faces of the chip-like electronic part 1. Because of limitations associated with the process commonly used to make the chip-like electronic part 1, the central electrodes 4 extend only partially on the other side faces of the chip-like electronic part. As a result, the central electrodes 4 do not extend entirely around the outer side surfaces of the chip-like electronic part 1.
The process for applying the central electrodes 4 is best understood with reference to FIG. 19. As shown herein, a groove 6 is provided in a paste base 5 which comprises an elastic body. The groove 6 is filled with a conductive paste 7 to form an elongated streak 8 of conductive paste 3. The chip-like electronic part 1 is held by a holder 9 so that one face of the chip-like electronic part 1 faces the streak 8 of conductive paste.
As best seen in FIG. 18, the chip-like electronic part 1 is an elongated parallel-piped structure having a main axis extending from end electrode 2 to end electrode 3. The central portion of the chip-like electronic part 1 is aligned with the streak 8 of conductive paste with the axis of the streak extending perpendicular to the central axis of the chip-like electronic part 1. The chip-like electronic part 1 is brought into contact with the paste base 5 and pressed against the paste base 5 to deform it and cause the conductive paste 7 to be applied to the outer surface of the chip-like electronic part 1 as shown by an imaginary line in FIG. 19. Although the conductive paste 7 extends across the entire side face of the chip-like electronic part 1 which faces the base 5, it only extends partway up the adjacent side faces of the chip-like electronic part 1.
The orientation of the chip-like electronic part 1 is then reversed so that its opposite face extends away from the holder and towards the paste base 5 and the process is repeated to place the conductive paste 7 on the opposite face (and particularly up the adjacent side faces) of the chip-like electronic part 1. Thereafter, the so applied central electrodes 4 are cured.
Instead of placing the conductive paste 7 in a groove 6 provided in the elastic paste base 5, the conductive paste may be applied (by printing or the like) on a flat face of a paste base 5 which can be either elastic or rigid. As another alternative, a reservoir of conductive paste located on one side of a slit plate can be extruded to the other side of the slit plate via the slit in the plate by applying pressure to the conductive paste.
The end electrodes 2 and 3 are formed by dipping the ends of the chip-like electronic part 1 into a tank of conductive paste.
As mentioned above, the central electrode 4 does not normally extend around the entire outer surface of the chip-like electronic part 1. However, it is preferable that it does to reduce unnecessary inductance components where the central electrode is used as a ground electrode.
It is not impossible to form the central electrode to extend around the entire circumference of the chip-like electronic part 1 using the process shown in FIG. 19. This result can be achieved by providing a sufficient amount of conductive paste to extend at least half way up the two side faces of the chip-like electronic part 1, for example, by making the groove deeper or pressing the chip-like electronic part 1 more strongly against the paste base 5. However, as shown in the sectional view of FIG. 20, overlap portions 12 are formed on flat end faces of the chip-like electronic part. These overlap portions 12 can hamper the mountability of the chip-like electronic part. Accordingly, it is preferable that a built-up portion, such as the overlap portion 12, not be formed at the central portion of any of the side faces of the chip-like electronic part 1.
This can be avoided by using a small enough amount of conductive paste that only one side of the chip-like electronic part receives the paste during any single application. However, this will necessitate four separate applications of the conductive paste which is not efficient.